1. Field of the Invention
The present invention relates to a fuel injection amount controller for engines, which controls the amount of fuel supplied to an engine of an automobile depending upon the operation condition (stoichiometric mode) at a stoichiometric air-to-fuel mode and the operation condition (lean mode) at a lean air-to-fuel ratio. More particularly, the invention relates to a fuel injection amount controller for engines which reduces torque shock at the time of acceleration and reduces torque shock caused by the correction of deceleration accompanying a change from the lean air-to-fuel ratio over to the stoicheometric air-to-fuel ratio.
2. Prior Art
The engines of automobiles have heretofore been employing a fuel injection amount controller which changes a stoichiometric mode over to a lean mode in order to suppress the consumption of fuel during the high-speed operation condition.
FIG. 6 is a diagram illustrating the constitution of a general fuel injection amount controller for engines. In FIG. 6, an engine 1 mounted on, for example, an automobile, takes in the air for supplying the fuel through an air cleaner 2, a throttle valve 3 and a surge tank 4.
A by-pass 5 is formed between the upstream side and the downstream side of the throttle valve 3. The by-pass 5 includes a solenoid valve 6 to adjust the opening degree of the by-pass 5.
During the idling operation of the engine 1, the throttle valve 3 is closed, and the opening degree of the by-pass 5 is adjusted by the solenoid valve 6, so that the air for combustion is supplied to the engine 1 in an amount corresponding to the opening degree of the by-pass 5.
The fuel in a fuel tank 7 is fed through a fuel pump 8, is adjusted to a predetermined injection pressure by a pressure regulator 9, and is injected through an injector 10 provided for each of the cylinders of the engine 1.
An ignition signal formed by an ECU (electronic control unit) 21 for every ignition timing is applied to a spark plug (not shown) provided for each of the cylinders of the engine 1 through an ignition drive circuit 11, an ignition coil 12 and a distributor 13.
Exhaust gases formed in the engine 1 after the combustion are released to the open air through an exhaust manifold 14 and the like.
A crank angle sensor 15 detects the rotational speed of the crank shaft of the engine 1, and forms pulse signals of a frequency corresponding to the rotational speed as crank angle signals CA.
The crank angle signal CA comprises a pulse signal which rises at BTDC (before top dead center) 75.degree. and breaks at BTDC 5.degree..
A cooling water temperature sensor 16 detects the cooling water temperature TW of the engine 1. An air-to-fuel ratio sensor 17 installed in the exhaust manifold 14 detects the concentration of oxygen in the exhaust gases as air-to-fuel ratio data AF. A pressure sensor 18 installed in a surge tank 4 detects the pressure in the intake pipe in terms of the absolute pressure and outputs a pressure detection signal of a voltage that varies depending upon the pressure Pb in the intake pipe.
An intake air temperature sensor 19 installed in the surge tank 4 detects the temperature TA of the air that is taken in. An idle switch 20 provided close to the throttle valve 3 detects the closure of the throttle valve 3 during the idling operation, and outputs an idle signal A.
Various detection signals from various sensors 15 to 19 inclusive of the idle switch 20 are fed to the ECU 21 as data representing the operation conditions of the engine 1.
The ECU 21 determines, based on the detection signals, the amount of fuel injection that varies depending upon the operation conditions, and controls the valve-opening time of the injector 10 to adjust the amount of the fuel injected into the engine 1. The ECU 21 controls the driving of the ignition drive circuit 11.
FIG. 7 is a block diagram illustrating in detail the constitution of the ECU 21. Here, a fuel control unit only is shown as an output unit.
In FIG. 7, the ECU 21 is constituted by a microcomputer 22, an analog filter circuit 23, an A/D converter 24 and a drive circuit 25.
The microcomputer 22 constitutes the main body of the ECU 21 and executes a variety of operations and judging processings.
The analog filter circuit 23 permits the pressure detection signal (intake pipe pressure Pb) from the pressure sensor 18 to be input to the A/D converter 24 while decreasing the ripples.
The A/D converter 24 successively converts the analog detection signal, i.e., intake air temperature TA, cooling water temperature TW, air-to-fuel ratio signal AF and intake pipe pressure through the analog filter circuit 23, into digital values, and sends them to the microcomputer 22.
The drive circuit 25 outputs a drive signal J for the injector 10.
The input ports of the microcomputer 22 are connected to the output terminals of the crank angle sensor 15, idle switch 20 and A/D converter 24.
The output ports of the microcomputer 22 are connected to the A/D converter 24 for sending reference signals and are further connected to the input terminal of the drive circuit 25.
The microcomputer 22 is constituted by a CPU 22A for executing a variety of operations and judgements, a ROM 22B storing the operation flow program of the CPU 22A, a RAM 22C functioning as a work memory, and a timer 22D to which the valve-opening time of the injector 10 has been set in advance.
Described below is a concrete operation of the ECU 21 by a conventional fuel injection amount controller for engines.
In the case of the device disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 275036/1990, when a deviation in the intake pipe pressure Pb in a predetermined period of time or between predetermined crank angles is greater than a predetermined value, it is so judged that the engine is in a transient condition (accelerating or decelerating condition), and the fuel injection amount is increased or decreased depending upon the deviation of the intake pipe pressure Pb.
According to the conventional device disclosed in the above-mentioned publication, the correction coefficient is not changed over depending upon the operation conditions at the time of acceleration or deceleration.
That is, when the operation condition is changed from the stoichiometric mode over to the lean mode during the acceleration operation, acceleration is judged due to a rise in the intake pipe pressure Pb accompanying an increase in the amount of the intake air, and the amount of the fuel is increased at the time of acceleration.
Furthermore, when the operation condition is changed from the lean mode over to the stoichiometric mode during the deceleration operation, the operation is judged to be the deceleration due to a decrease in the intake pipe pressure Pb accompanying a decrease in the amount of the intake air, and the amount of the fuel is decreased at the time of deceleration.
When a deviation in the pressure in the intake pipe becomes greater than a predetermined value as described above, it is so judged that the engine 1 is in a transient operation condition (accelerating or decelerating condition), and the amount of the fuel supplied to the engine 1 is increased or decreased depending upon a deviation .DELTA.Pb in the intake pipe pressure Pb.
When the stoichiometric mode is changed over to the lean mode at the time of acceleration, however, the air-to-fuel ratio is becoming rich due to an increase in the fuel injection amount. Therefore, the stoichiometric air-to-fuel ratio is not smoothly changed over to the lean air-to-fuel ratio, giving rise to the occurrence of an acceleration shock.
When the lean mode is changed over to the stoichiometric mode at the time of deceleration, furthermore, the air-to-fuel ratio is becoming lean due to a decrease in the fuel injection amount. Therefore, the lean air-to-fuel ratio is not smoothly changed over to the stoichiometric air-to-fuel ratio, giving rise to the occurrence of a deceleration shock.
FIG. 8 is a timing chart illustrating the operation for correcting the amount of the fuel by the above-mentioned conventional device, and illustrates changes in the intake pipe pressure Pb, in the opening degree .theta. of the throttle valve 3, in the deviation .DELTA.Pb in the pressure, in the fuel injection amount QF and in the air-to-fuel ratio A/F with the passage of time.
In FIG. 8, a stoichiometric mode section T1 is changed over to a lean mode section T2 at a timing t1, and the lean mode section T2 is changed over to a stoichiometric mode section T3 at a timing t2.
The throttle opening degree .theta. is opened at a timing t3 as the accelerator pedal is depressed, and the throttle opening degree .theta. is closed at a timing t4 as the accelerator pedal is released.
In the stoichiometric mode sections T1 and T3, the air-to-fuel ratio A/F is controlled to be a stoichiometric air-to-fuel ratio (.apprxeq.14.7). In the lean mode section T2, the air-to-fuel ratio A/F is controlled to be a lean air-to-fuel ratio (&gt;14.7).
At the timing t1 when the stoichiometric mode section T1 (operation condition at the stoichiometric air-to-fuel ratio) is changed over to the lean mode section T2 (operation condition at the lean air-to-fuel ratio), the amount of the fuel is increased at the time of acceleration and, hence, the air-to-fuel ratio A/F becomes rich and rapidly decreases.
Accordingly, the stoichiometric air-to-fuel ratio is not smoothly changed over to the lean air-to-fuel ratio, and an acceleration shock takes place.
At the timing t2 when the lean mode section T2 (operation condition at the lean air-to-fuel ratio) is changed over to the stoichiometric mode section T3 (operation condition at the stoichiometric air-to-fuel ratio), the amount of the fuel is decreased at the time of deceleration and, hence, the air-to-fuel ratio A/F becomes lean and rapidly increases.
Accordingly, the lean air-to-fuel ratio is not smoothly changed over to the stoichiometric air-to-fuel ratio, and a deceleration shock takes place.